A common drawback of known light guides used for light devices of motor vehicles is the fact that a certain part of the light emitted by the light sources is not used or that the required shape of the output surface of the light guide does not support efficient use of the emitted light, which reduces the light efficiency of the light guide. In the field of the design of light guides and light-guiding systems, there is a permanent effort to propose such designs that will bring an increase of their light efficiency and ensure homogeneity of the output light beam.
The documents U.S. Pat. No. 7,401,948B2 and WO2008069143A1 disclose collimating elements that comprise a central recess for efficient binding of light rays from the light source to the body of the collimating element. In principle, in one recess of a collimating element just one LED light source can be used. The body of these collimating elements comprises a central lens to direct emitted light rays in a straight direction as well as lateral segments to direct emitted light rays in an indirect direction.
Examples of known designs of a light guide striving to increase the light efficiency are the solutions described in the documents JP06082264B2 and CZ20050096A3. These solutions are based on using configured reflective surfaces for total reflection of light rays and sending them to the required direction. However, a disadvantage of this solution is that efficient use of light emitted by the light sources is not made possible because maximum binding of light rays emitted by the light source is not enabled. Another disadvantage is the shape of the light guide, which is not adaptable to the mechanical design of the light device.
From the documents FR2966224A1 and US20150247613A1, lighting and/or signaling devices for a motor vehicle are known that comprise a light source and a light-guiding plate that has a surface for the entry of light rays and an output edge/surface and is configured to spread light rays towards the output surface. The light-guiding plate comprises a collimator with a surface for the entry of light rays emitted by the light source and with a transitional surface for the output of the collimated light beam from the collimator into the body of the light-guiding plate, this collimator being positioned with respect to the plate in such a way for the axis of the collimated beam to be oriented in the thickness direction of this plate, preferably in the vertical direction. The light-guiding plate comprises reflective means which light rays from the transitional surface of the collimators are sent to. The reflective means is designed as an array of reflective surfaces configured to direct rays of the collimated beam towards the output surface, i.e. to deflect light rays from the vertical plane to the horizontal plane. The reflective means is designed as an array of at least three reflective surfaces wherein a part of light rays is directly sent to the output surface, another part of light rays being routed to the output surface indirectly. Light rays are first directed from the reflective surfaces towards the lateral edges of the light-guiding plate where reflective surfaces adapted to direct light rays towards the output surface of the light-guiding plate are situated. The first disadvantage of this solution is uneven distribution of light intensity on the output surface of the light-guiding plate as at least two reflective surfaces of the reflective means have a common edge in each case, i.e. they are not spatially offset, i.e. they have a constant shape of a sector of a circle, and on the output surface, patterns are projected in the form of discontinuous regions with an unsymmetrical shape that do not respect the shape of the output surface. Thus, the light guide can only project light patterns having the shape of a sector of a circle or a shape similar to a sector of a circle through its output surface. Another disadvantage is that the size of the reflective surfaces of the reflective means cannot be changed to adapt the optical concept to the mechanical design of the lighting device. The third disadvantage is the fact that the ratio of the width to the thickness of the light guide is fixed and the shape of the collimator determines the shape of the reflective means and thus the shape of projected patterns on the output surface, which makes redistribution of the intensity of light emitted from individual reflective surfaces of the reflective means through the reflective means impossible and it is not possible to divide light into two separate light guides either.
At present, vehicle designers often require that the output light surfaces of some function having a designer shape be as thin as possible, on the order of several millimeters. However, this requirement encounters several technical problems. For example, from the document CZ201600183, a light guide is known that comprises at least one transitional surface that is, in the profile of the light-conductive body towards the output surface, inclined to the longitudinal axis of the profile while a collimating element is situated at the input surface and the output surface can be defined as a thin one. A disadvantage of this solution is the fact that the dimensions of the light guide must be selected in such a way that either the output surface is thin, but the light efficiency of the light guide is not high, or the light efficiency is high and the output light surface is not as thin.
A light-conductive system is known from the document JP5692517 that comprises a planarly shaped light guide of a plate-like shape and a collimating element having the form of a rotary body. The light guide and the collimating element form an integral body that is made from an optically transparent material and is used to guide light rays emitted by the light unit comprising at least one light source, e.g. LED. The outer shell of the light guide is fitted with an array of reflective surfaces to create light patterns on the output surface of the light guide. Two lateral reflective surfaces situated at the collimator form a reflective means to direct light rays to two separate assemblies of reflective surfaces gradually directing light rays to the output surface. For the use of a very thin planar light guide, e.g. with the thickness of 2 mm, the smallest possible collimating element with the diameter of 4 mm can be used. In case of a long output surface of the light guide, a higher number of collimating elements and light sources needs to be used. Another disadvantage of this solution is the fact that the light beam gets divided especially over the center of the collimating element, which may cause a loss of efficiency and even small production defects/deviations can result in a significant loss of efficiency.
The object of the present invention is to solve the issue of increasing the light efficiency of collimating elements connected to a very thin, planarly shaped light guide without a large number of light sources having to be used to ensure the required light characteristic. Thus, the task of the invention is to propose a light-conductive optical system that makes it possible to fulfill the required light function, including high light efficiency and even distribution of the light intensity on the output surface when a thin, planarly shaped light guide is used. Another object is to make sure that the light-conductive system is adaptable to requirements resulting from the mechanical and optical design of the lighting device with acceptable financial requirements for the production.